Stereo-Active Lone Pairs Induced Second Harmonic Generation Responses and Electrocatalytic Activity in Hybrid Material.

Abstract

The lone pair electrons in the electronic structure of molecules have been a prominent research focus in chemistry for more than a century. Stable s2 lone pair electrons significantly influence material properties, including thermoelectric properties, nonlinear optical properties, ferroelectricity, and electro(photo)catalysis. While major advances have been achieved in understanding the influence of lone pair electrons on material characteristics, research on this effect in organic-inorganic hybrid materials is in its initial stage. In this work, we successfully obtained a novel organic-inorganic hybrid multifunctional material incorporating Ge with 4s2 lone pair electrons, (MeHDabco)2[GeBr3]4-H2O (MeHDabco=N-methyl-1,4-diazabicyclo[2.2.2]octane) (1). Driven by the stereochemically active lone pair electrons on the Ge2+, 1 crystallizes in the noncentrosymmetric space group P21 at room temperature and exhibits good second harmonic generation (SHG) responses. Interestingly, 1 also shows electrocatalytic activity for the hydrogen evolution reaction (HER) due to the existence of lone pair electrons on Ge2+ cations. The electrochemical experiment combined with the density functional theory (DFT) calculations revealed that the lone pair electrons act as both an active site for proton adsorption and facilitate the ionization of water. This work not only emphasizes the important role of lone pair electrons in material properties and functions but also provides new insight for designing novel Ge-based multifunctional hybrid materials.